The manufacturing of field emission display (FED) based on the principle of field emission has been positively researched and developed since the field emission electron property was found. Meanwhile, since the liquid crystal display (LCD) has the advantageous slim and planar structure, the application of the field emission display to the backlight module for the LCD is also widely developed. The field emission display (FED) is superior to the conventional cold cathode fluorescence lamp (CCFL) for LCD in many aspects, including the brightness, response speed, range of vision, etc. Generally speaking, the field emission display is very suitable for use as a backlight module. However, the conventional field emission display is hindered from being commercialized within a short time by several tough problems in the manufacturing process thereof.
FIG. 1 is a conceptual diagram of a conventional vertical type field emission backlight module, which includes a cathode 20 having a field emitter 21, on which a carbon nano material is grown and an array of spindles is formed; an anode 10 that is an indium tin oxide (ITO) glass coated with a layer of fluorescent powder 11, and a gate 22 provided closed to a top of the cathode 20. Due to a high field between the cathode 20 and the anode 10, the field emission electrons are emitted from the field emitter 21 of the cathode 20 in a vacuum space enclosed in the module, and impact the fluorescent powder 11 on the anode 10 for the fluorescent powder 11 to produce light. The gate 22 is connected to a relatively small positive electricity, so as to attract the cathode to increase the electron emissivity.
The above-described conventional vertical type field emission backlight module is prevented from commercializing due to the following disadvantages: (1) It requires a spacer 12 to control a vertical distance between the cathode 20 and the anode 10; (2) since the allowable tolerance for the module is very small, considerations in structural design and good yield must be taken when the module is applied to a large area; moreover, it is also very difficult to control the evenness of an overall brightness when the module is applied to a large area; (3) in the event the carbon nano material is not evenly grown on the field emitter 21 at the cathode 20, there would be some areas on the cathode 20 that do not have emitted electrons, resulting in dark spots on the fluorescent powder 11; (4) since the light from the fluorescent powder 11 would be blocked by the anode 10, the anode 10 must be an expensive light-transmittable conducting glass made of indium tin oxide; (5) the gate 22 also requires additional manufacturing cost; and (6) the emitted electron beam tends to be out-of-focus and results in a low contrast image.